Unable to communicate with ESP32 Pico-D4 (particular batch)

[zjustin]

Hi Gurus

I'm encountering something rather strange.

I have a PCB design which already gone through the first round of test production (I produced 30PCB, and assembled 6 of them with ESP and all my other components), everything seems to be okay, I have 6 touch points on the PCB which can be connected to a FTDI cable to communicate with my Arduino IDE both for flashing and serial communication.

However when I assemble the 2nd batch(6 pc again), using the same PCB produced above, all the boards failed to be able to communicate to my PC, there seems to be no serial communication at all, even when I manually pull GPIO 0 to GND, the serial connection does not give the standard "boot loader msg". when I measured the ESP32, the U0RXD/U0TXD are connected properly to my computer. the VDD_SDIO has 3.2V , so ESP is being powered.

since the ESP32 chip are from the same batch of purchase as the first round of production. I am really getting lost as what could happen?

same PCB design, from the same PCB production batch, same ESP from same batch purchase (so does most of other components).
just two different assembly batch.

Is there possibility that all 6 ESP32 chip is faulty in the new batch of assembly ? anything else I could check ?
help needed.

[ESP_Sprite]

Hard to say... perhaps put a scope on xtal_[np]_nc and see if there's a 40MHz signal on either of those pins? Also see if VDD_SIO has any voltage?

[jkingdon]

Did you dry them out before assembly? Picos are msl3 so vulnerable to damage if kept around a while and then heated.